Electrolytic cells of the liquid electrode type



April 11, 1950 B. w. HIRSH ETAL 2,503,337

ELECTROLYTIC CELLS OF THE LIQUID ELECTRODE TYPE Filed Sept. 15, 1946 2 Sheets-Sheet 1 FIG. I

Benjamin W. Hirsh d Charles Carter INVENTORS BY MW, M .Mm

April 11, 1950 B; w. HIRSH ET AL 2,503,337

ELECTROLYTIC CELLS OF THE LIQUID ELECTRODE TYPE Filed Sept. 13, 1946 2 Sheets-Sheet 2 I4 I i l2 l2 i l6 G 4 l7 5 o IO 10min W. Hirsh d rles Cur VENTORS Patented Apr. 11, 1950 ELECTROLYTIC CELLS OF THE ELECTRODE TYPE LI UID Benjamin Woolf Hirsh, Welwyn Garden City, and Charles Carter, Liverpool, England, assignors to Imperial Chemical Industries Limited, a corporation of Great Britain Application September 13, 1946, Serial No. 696,694 In Great Britain August 27, 1941 Section 1, Public Law 690, August 8, 1946 Patent expires August 27, 1961 This invention relates to improvements in electrolytic cells having a liquid electrode, and more particularly to improvements in cells of this type for the electrolysis of aqueous solutions of alkali metal chlorides, using a flowingmercury cathode.

Many forms of apparatus have been proposed for the electrolysis of alkali metal chlorides using a mercury cathode. One which has been found suitable comprises 'a covered trough-shaped vessel having a smooth plane bottom, long in comparison with its width, arranged to be at a slight angle to the horizontal so that the mercury cathode can be caused to flow along the plane surface of the bottom as a continuous sheet. As electrolysis proceeds the mercury is converted into an amalgam, increasing in strength as it passes down the cell. However, it is convenient-to refer to the electrode as being mercury, and the word mercury is so used in the-present specification unless the context requires the narrowermeaning. In cells of this type, the anodes are usually formed of graphite plates or blocks which are so fixed on carbon rods passing through the cover of the cell that their undersurfaces are arranged substantially parallel to, and but a short distance above, the mercury cathode. The cover is joined to the cell in a gas-tight manner, e. g., it may be fixed to the trough by bolting it to the sides using a suitable jointing material, to render the seal gas-tight, or if it is sufficiently heavy the cover may make its own joint by pressing on suitable plastic luting material between it and the sides. The cover is also provided with outlet pipes through which chlorine evolved at the anode is drawn off. In using the cell, mercury'and an alkali metal chloride solution are causecl'to flow through the cell at rates which depend on the working conditions; the linear flow of'the alkali metal chloride solution inthe cell is comparatively slow, in general it is less than 2 cms. per second and usually between 0.25 and 1cm. per second. The level of the solution in the cell is adjusted so that it does not reach to the lid,

thus leaving a considerable space where chlorine evolved at the anode can collect, from which it may be drawn ofit through the pipes provided. The amalgam to which the mercury cathode is converted and spent brine are drawn oh by suitably placed conduits.

With continued use, the undersurfaces of the graphite plates wear away, and to maintain. efiie cient working conditions, it is customary from time to time to readjust the height of the graphite plates to compensate for this wear. -This has hitherto necessitated breaking and remaking the 5 Claims. (Cl. 204250) seal between the cover and cell sides on the occasion of each readjustment, and thus made it necessary to interrupt the electrolyticprocess.

This invention has particular reference to the operation of the electrolytic processes which are described and claimed in our copending application, Serial No. 695,804, entitled Electrolysis," filed September 9, 1946.

In this application, there is described the marked advantages which are obtained in the electrolysis of aqueous solutions of sodium and potassium chlorides using a mercury cathode with superposed solid electrodes when the electrolyte is caused to flow through the inter-electrode space with a high velocity. In the known kinds of electrolytic cells for the electrolysis of aqueous solutions the condition of high velocity flow in the inter-electrode space is difilcult to achieve, since the electrolyte is able to flow in the space between the upper surface of the solid electrodes and the cover of the cell.

A principal object of this invention is the provision of electrolytic cells of the liquid electrode type which are specially welladapted to the electrolysis of aqueous solutions, wherein high velocity flow of the electrolyte in the inter-elemtrode space is involved. A further object is the provision of cells of the subject type which are well adapted to electrolysis of aqueous solutions under super-atmospheric pressure. Another object is the provision of such cells,'in which flow of electrolyteis permitted only in the inter-electrode space between the solid anode and the flowing cathode. A still further object is the provision of cells which make possible the electrolysis of aqueous alkali metal chloride solutions to form chlorine at a minimum operating voltage and with very high efficiency. Further objects and the entire scope of applicability of the present invention will become apparent from the detailed description given hereinafter.

These objects are accomplished according to the present invention by the use of a cell of the liquid electrode type in which the solid electrodes in the upper part of the cell are so arranged that substantially the whole of the cross-section of the cell above the inter-electrode gap is inaccessible to longitudinal flow of electrolyte. Additionally these cells include means external of the cell for adjusting the height of the interelectrode space and means for sealing the cell from the surrounding atmosphere.

Accordingly the present invention consists in an electrolytic cell comprising two portions, i. e.,

- a base which provides an elongated plane mercury electrode carrying surface and a cover which carries an assembly of solid electrode material having the lower surface but a short distance above and substantially parallel to the upper surface of the mercury electrode and arranged to permit the withdrawal of fluid from the inter-electrode i surrounding the mercury carrying surface and adapted to contain mercury and the upper portion comprises a cover into which the solid electrode assembly is fitted and which is provided with a rigid skirt depending below the solid electrode assembly and adapted to fit loosely in the channel in the trough-shaped vessel when the cover is in position.

Advantageously also, the channel is provided with a resilient deformable packing adapted to contact both the skirt and a wall of the channel and thus assist the formation of an improved seal; suitably the packing is of sponge rubber, or is an endless inflated rubber tube.

The invention is especially adapted for use in a. cell of the type having a flowing mercury cathode, the channel forming part of the seal being then around the perimeter of the bottom of the cell over which the mercury cathode flows, this mercury helping to form the seal. As in known constructions, the solid electrode of such a cell may be suspended from the cover of the cell. There are also provided the appropriate electrical connections and means for introducing and removing the electrolyte, mercury, and the products of electrolysis. Suitably, the skirt and the cover are of ebonite, concrete, or other insulating material resistant to chlorine, or they may be of metal, e. g., steel, coated with such protective insulating material. In an advantageous form of the invention, the trough-shaped body, being maintained out of contact with the electrolyte, may be constructed from a suitable metal, such as steel. The skirt extends down into the channel, and between the inner wall of the channel and the skirt an endless band of sponge rubber or an endless inflated rubber tube is fitted which presses against both the channel wall and the skirt.

In combination with the above features, we find that considerable advantages can be attained by replacing the graphite plates which are normally used as anodes in electrolytic cells using flowing mercury cathodes by graphite blocks which fit closely to the cover and inside wall of the skirt, and which are provided with suitable vents to permit the escape of the gaseous prodnets of electrolysis, each vent extending to a height above the cell greater than the head of electrolyte beneath it. An apparatus is thereby provided well suited for carrying out the process described in the aforesaid copending application.

In using a cell according to this invention, mercury and electrolyte are caused to flow through the trough-shaped vessel and the current is switched on. The mercury cathode will not only flow over the plane bottom of the vessel but will also fill the space in the channel not occupied by the rubber tube or the skirt, thus reinforcing the seal to prevent escape of chlorine, and protecting the rubber packing against corrosion. Nevertheless, adjustments can be made in the position of the cover, and thus, of the anode attached to it, and it will be possible to make these adjustments without interrupting the electrolysis. By providing the resilient deformable packing in the channel, the diversion of the mercury flow from the plane surface to the channel can be reduced to small proportions. It will be apparent that this latter desirable condition can more readily be realised if the thickness of the sides of the cover is only slightly less then the width of the channel.

A more comprehensive understanding of the structures of this invention may be had by reference to the accompanying drawings, which diagrammatically, and not to scale, illustrate specific embodiments of the invention.

In the drawings:

Figure 1 is a vertical section along the line l-I of Figure 3, showing a specific form of our electrolytic cells.

Figure 2 is a vertical section of another form of our cells which incorporates different means for removal of chlorine formed in the electrolysis than the structure illustrated in Figure 1.

Figure 3 is a top plan view partly in section of a cell of the type shown in Figure 1.

In the drawings in which similar numerals refer to similar parts, the cells consists of a trough-shaped vessel I, having a plane bottom over which can flow mercury indicated at 2, and above it can flow, co-current with the mercury, aqueous electrolyte 3. Around the perimeter of the plane bottom is a channel la. Each cell has a cover 4 carrying a number of solid anode blocks 5, depending from carbon rods 8 which pass through openings to the cover and through which current is supplied to the anodes by means not shown. In the drawing, the joint of the rods with the cover is shown to be sealed by sealing composition 1, but any other suitable method of rendering the joint gas-tight may be used.

Depending from cover 4 is a skirt 8, the lower edge of which dips into the channel la, and an endless inflated rubber tube 9 is disposed between the inner wall of the channel and the skirt. When the cell is in operation, the channel will be filled with mercury, and the assembly of the skirt 8 and tube 9 will form a seal reinforced by the mercury. The rubber tube will thus be protected from the action of the electrolyte, which will con tain dissolved chlorine, by the layer of mercury above it. From each side of cover 4 project laterally a number of lugs In (one on each side being shown), each of which rests on the top of the cell body I. The vessel I is suitably made of steel. but concrete may be used while the cover 4 and skirt 8 may be made of steel covered with ebonite. Appropriate means (not shown) for supplying and withdrawing mercury and electrolyte are also provided at the appropriate ends of the cell, and take the form of orifices in that part of the cell between the end of the anode and the channel la.

Tube 9 is connected with means (not shown) by which the interior of the tube can be evacuated or filled with water under pressure. By the use of this inflatable tube, a seal capable of withstanding high pressures is obtained which seal can be repeatedly made or broken as necessitated by the operation of the cell. Advantageously, cold water is used as the pressuring means for the tube 9 and circulation of the water is maintained,

so as to keep the sealing tube cool and, thus, considerably extend its life.

Referring in detail to the Figures 1 and 3., the anode blocks 5 are designed to fill substantially the whole of the cross-section. of the cell above the level oi their undersurface, except that between adjacent blocks there is a gap extendin across the whole cross-section of the cell in which chlorine can rise to one of a number of gas offtakes ll (one of which is shown), one being situated above each gap. Each ofi-take rises to a height above the cell greater than the head of brine immediately beneath it before joining a header (not shown), and thus, together with the gaps immediately beneath it, forms an independent vent by which chlorine can be drawn off from the cell.

Because the blocks fill substantially the whole of the space above the inter-electrode gap and the height of the various o'iT-takes are designed as described above, no alternative path for flow of the electrolyte is provided, and the electrolyte is compelled to flow between the electrodes in spite of the relatively high resistance due to the interelectrode gap.

In putting such cells into operation, tube 9 is deflated and the bottom of the vessel 1 is flooded with mercury so as to fill channel Ia and thus cover the tube 9; the lid 4 is then lowered into place with the bolts 12 in a position which gives approximately the correct inter-electrode gap and tube 9 is inflated. The skirt 8 will then bear against tube 9 and thus seal the space inside the cell from the outside atmosphere. Adjustments in the height of the anode can be made as required by movement of the bolts 12; if bolts 12 are raised in lugs I0, the weight of the anode assembly will cause the skirt 8 to deform rubber tube 9 and thus allow the inter-electrode gap to decrease. If, initially, the inter-electrode gap is too small, it can be raised by lowering bolts 12 in the lugs l and the resilience of tube 9 ensures that the seal will still be maintained. Adjustments can be made in a similar manner during the use of the cell when the anode gap becomes too large as the result of wear.

Referring in detail to Figure 2, there is shown the base of the cell l, carrying the flowing inercury cathode 2 above which is the aqueous electrolyte 3. The cell possesses a lid or cover 4 with integral depending skirts 3 extending into channel la in the base i. The solid anode is suspended by tubes M which extend through the lid 4 into the solid anode 5 and terminate at the top I! of a vertical slot running the full width of the anode 5 and extending upwards from the lower surface of the anode through part of its thickness. Thus the hollow tubes I4, supporting the anode, furnish communicating passage ways with the inter-electrode space so as to permit removal of chlorine formed in the electrolysis from the inter-electrode space.

In the construction illustrated in Figures 1 and 3 flow of the electrolyte is restricted to the interelectrode space by the fact that the anode 5 is of such size that it conforms very closely to the lid 4 and skirts 8 of the cell so that flow of the electrolyte cannot take place, except in the interelectrode space. Restriction of the electrolyte flow to the inter-electrode space is accomplished by different means in the structure shown in Figure 2. Thus, the anode 5 in this structure is not as conforming as in the structures shown in Figures 1 and 3, so that a greater space exists between the sides and top of the anode and the cover 4 and depending skirts 8. This space is filled with chlorine resisting material l6, preferably of a resilient nature, e. g., sponge rubber coated with neoprene, polythene, chlorinated polythene, or the like.

The cells provided by this invention are adapted for high-speed brine flow and permit brine to be introduced into the cells at superatmospheric pressure. The height above the bottom of the cell to which the passages leading off chlorine, e. g., tubes H in Figures 1 and 3 and tubes M in Figure 2, must extend will be determined by the head of brine at the cell inlet. This head will, in turn, depend on the size of the interelectrode gap and the velocity of the brine. With satisfactory operation with high speed brine conditions, the head of brine corresponds to about 4; inch per foot length of cell. It is convenient to carry all the passages to the same height, although it will be appreciated that the height of the passages at the end by which the brine leaves will not need to be as great as at the other end.

As many and varied modifications of the subject matter of this invention will become apparent to those skilled in the art from the detailed description given herein, it should be understood that this invention is to be limited only in accordance with the appended claims.

We claim:

1. An electrolytic cell of the mercury cathode type capable of operating at high electrolyte Velocities, comprising an elongated rectangular trough-like base having a flat bottom section which carries a mercury electrode upon its up per surface, a longitudinal channel in said base along the lengthwise sides of said bottom section, a plate-like cover extending across the cell beyond the edges of the mercury electrode having an integral skirt depending therefrom into said channel, an inflated, resilient tube disposed between a side of the channel wall and said skirt, a solid electrode extending across the inside of the cell within the confines of said cover, said solid electrode being carried by the cover with its undersurface disposed a short distance above the upper surface of the mercury electrode and substantially parallel thereto, conduits for withdrawal of gas from the inter-electrode space extending through said solid electrode and said cover, all free space within the inner confines of said cover above the level of the anode undersuriace, aside from said conduits, being filled with solid material, and means external of the cell for adjusting the inter-electrode space by movement of said cover relative to said base. 7

2. A cell as claimed in claim 1, in which there is a packing of chlorine-resistant, plastic material between the inner surfaces of the cover and the outer top and side portions of said anode.

3. A cell as claimed in claim 1, in which said anode fills the entire space within the inner confines of said cover.

4. A cell as claimed in claim 1, in which said gap adjusting means comprises an outside threaded section carried in an inside threaded lug extending -from said cell cover.

5. A cell as claimed in claim 1, in which said passages connecting the gas withdrawal conduits with the inter-electrode gap are slots extending across the cell formed by free space between the ends of two of the solid anodes.

BENJAMIN WOOLF HIRSH. CHAS. CARTER.

(References on following page) REFERENCES CITED The following references are of record in the N be file of this patent: 26,504

UNITED STATES PATENTS 6 316,694 Number Name Date 173520 1,346,849 Shaw July 20, 1920 1,575,627 Heinze Mar. 9, 1926 2,104,678 Sorensen Jan. 4, 1938 FOREIGN PATENTS v Country Date Great Britain 1912 Great Britain Aug. 8, 1929 Germany July 26, 1906 

1. AN ELECTROLYTIC CELL OF THE MERCURY CATHODE TYPE CAPABLE OF OPERATING AT HIGH ELECTROLYTE VELOCITIES, COMPRISING AN ELONGATED RECTANGULAR TROUGH-LIKE BASE HAVING A FLAT BOTTOM SECTION WHICH CARRIES A MERCURY ELECTRODE UPON ITS UPPER SURFACE, A LONGITUDINAL CHANNEL IN SAID BASE ALONG THE LENGTHWISE SIDES OF SAID BOTTOM SECTION, A PLATE-LIKE COVER EXTENDING ACROSS THE CELL BEYOND THE EDGES OF THE MERCURY ELECTRODE HAVING AN INTEGRAL SKIRT DEPENDING THEREFROM INTO SAID CHANNEL, AN INFLATED, RESILIENT TUBE DISPOSED BETWEEN A SIDE OF THE CHANNEL WALL AND SAID SKIRT, A SOLID ELECTRODE EXTENDING ACROSS THE INSIDE OF THE CELL WITHIN THE CONFINES OF SAID COVER, SAID SOLID ELECTRODE BEING CARRIED BY THE COVER WITH ITS UNDERSURFACE DISPOSED A SHORT DISTANCE ABOVE THE UPPER SURFACE OF THE MERCURY ELECTRODE AND SUBSTANTIALLY PARALLEL THERETO CONDUITS FOR WITHDRAWAL OF GAS FROM THE INTER-ELECTRODE SPACE EXTENDING THROUGH SAID SOLID ELECTRODE AND SAID COVER, ALL FREE SPACE WITHIN THE INNER CONFINES OF SAID COVER ABOVE THE LEVEL OF THE ANODE UNDERSURFACE, ASIDE FROM SAID CONDUITS, BEING FILLED WITH SOLID MATERIAL, AND MEANS EXTERNAL OF THE CELL FOR ADJUSTING THE INTER-ELECTRODE SPACE BY MOVEMENT OF SAID COVER RELATIVE TO SAID BASE. 